Conjugative shift of horizontal gaze towards the affected hemisphere is a well-recognized occurrence in AIS patients, as first described by Jean Louis Prevost in 1865. Commonly referred to as conjugate eye deviation (CED), it is often assessed in clinical stroke severity diagnostic tools such as the National Institute of Health Stroke Scale/Score (NIHSS).
CED appears in more than 55% of the computerized tomography (CT) scans taken upon hospital admission in AIS patients. Moreover, studies evaluating the clinical significance of CED in AIS patients have repeatedly demonstrated that the degree of deviation is associated with stroke severity at hospital intake and poor prognostic outcomes, with the direction of deviation typically presenting ipsilateral to the affected brain hemisphere. CED-causing lesions in AIS patients generally reflect damage to cortical areas involved in the control of spatial attention, eye movements, and the frontal eye fields. These findings suggest that CED identification may be a useful tool in the assessment of AIS severity and infarction location, as well as prognostic outcome.
There has previously been no clear consensus on the threshold at which CED is thought to become a significant observation, but is has been noted a high specificity (95.9%) for a CED of >11.95° on CT imaging following acute infarct. Despite being highly specific, only a 17% sensitivity has been noted. This in turn means an 83% false negative rate, representing a failure to detect the majority of AIS cases based on this criteria. Thus, while this threshold may be a helpful additional tool in the detection of acute infarct, its clinical utility remains to be improved.
Additionally, it appears that that the utility in identifying CED is negated in patients with large hypoattenuation, as is often the case in patients with a CED of >11.95°. Specifically, past research has demonstrated that CED recognition on CT scan does not increase reader identification of acute ischemic hypoattenuation if four or more Alberta Stroke Program early CT score (ASPECTS) zones are involved. Similarly, NIHSS and CED degree are linked such that a patient with a CED of >11.95° will likely present with a wealth of other identifiable symptoms, which further decreases the unique contribution of CED in AIS diagnosis. Taken together, this research suggests that CED identification at the currently established threshold may not be a useful tool in the diagnosis of AIS.
As noted, CED's strong association with AIS gives it potential as a useful diagnostic tool. Nonetheless, prior research has also demonstrated the limitations of CED as it stands, which emphasizes the importance of improvements to the tool. Accordingly, there exists a need for an improved system and method for increasing the efficacy of CED as a tool for the identification of AIS.